1. Field of the Invention
This invention relates to an image storage system which stores in a storage medium digital data corresponding to an image, and outputs the digital data stored in the storage medium.
2. Description of the Prior Art
Recently, small-sized semiconductor memories having large capacity have been offered relatively inexpensively in accordance with the rapid progress in semiconductor technology. Keeping pace with this situation, in the field of apparatuses for consumer use, there have been produced video cassette recorders (VCR's) utilizing memories (hereinafter termed frame memories) each of which can store color television signals for one picture frame, and the like. There have also been announced electronic cameras of a type in which a memory pack is detachably mounted in a video camera, and color video signals for one field or one frame corresponding to a still picture imaged by the camera are stored in a memory within the memory pack.
If it is intended to increase the number of picture frames which can be stored without increasing the size of a memory pack in this kind of electronic camera, it is necessary to reduce the amount of data for one picture frame. However, since a mere reduction in the amount of data results in a deterioration of picture quality, it is desirable to reduce the amount of data by a high-efficiency coding technique which is well known in the field of digital signal processing.
In accordance with the tendency toward smaller memories having larger capacity and improvements in data compression techniques, it becomes possible to increase the number of still pictures which can be stored within a single memory, and it is expected that the number will become larger.
Suppose that still pictures in the quantity of about 300 picture frames are, for example, stored in one memory pack. When these pictures are dubbed to another memory pack as digital signals, a time of 10 seconds or more is needed even if the dubbing is performed at a rate of 1/30 second for one picture frame. Accordingly, when it is intended, for example, to provide copy of a plurality of memory packs, a long time is required for dubbing. However, if the data rate for write/read is simply increased, it is necessary to match the operation timings of imaging means at the moment of a photographing operation with the timings of a reproduced output for a still picture at the moment of a reproducing operation. Furthermore, digital signal processing at the moment of photographing and reproducing operations must be performed at high speed, and hence the digital signal processing is restricted in time.